Understanding a new EPA fuel economy ratings system.

By Jim Gorzelany

Although automotive engineers are constantly exploring ways to help boost the fuel economy of tomorrow's cars and trucks, expect virtually every new car and truck to post noticeably lower fuel economy ratings for the 2008 model year. That's because the federal Environmental Protection Agency is switching to a new method of evaluation that's designed to better reflect a vehicle's "real world" fuel consumption.

As just about any astute owner has observed, today's vehicles achieve nowhere near the fuel economy ratings provided by the EPA (these estimates are required by law to be posted on most new-models' window stickers). Now 30 years old, energy experts say the EPA's testing procedures are both out of date and out of sync with 21st Century vehicles, traffic patterns and driving habits.

"This year alone, American consumers will spend about $20 billion more on gasoline than they would expect based on the fuel economy stickers," says a spokesperson for the Union of Concerned Scientists.

The EPA tests cars under rigidly controlled circumstances in a laboratory that run contrary to the way most of us drive. Each model is tested on what's called a dynamometer, which is like a treadmill for cars, and is run through two standardized driving schedules, one each to simulate city and highway motoring. The engine's exhaust gases are collected and analyzed to calculate the amount of fuel that's being burned.

Unfortunately, the current cycles assume conservative motoring habits that might make the proverbial little old lady driving to church seem aggressive by comparison. What's more, they're conducted only at moderate atmospheric temperatures and with the vehicles' air conditioning and other accessories turned off.

While the general procedures under which cars are tested won't change, the test cycles themselves will be altered along with the manner in which the EPA ultimately estimates a vehicle's fuel economy.

Initially a "fudge factor" will be applied to the current evaluation process during a transitional period, though by 2011 fuel economy for all models will be measured according to three extra test cycles in addition to the current city/highway assessments. These will include simulations that account for high-speed and aggressive driving. Also, a vehicle's performance in cold weather will be replicated, as will running a car or truck at high ambient temperatures for extended periods with the air conditioning switched on.

Under the new testing procedures, the city miles-per-gallon estimates for most vehicles would drop 10 percent to 20 percent, depending on the vehicle, the EPA advises, while highway mpg estimates would generally drop by a factor of five to 15 percent.

By the EPA's own projections, this means the subcompact Nissan Versa, which for 2007 is estimated at 30-city/34-highway mpg will be given a revised rating of 26/31 for 2008. At the other end of the spectrum, the larger V-6-powered Dodge Charger sedan that now garners a 2007 rating of 19/27 drops to 17/24 the next year. Other examples include the full-size Chevrolet Tahoe sport-utility vehicle's 16/22 mpg estimate will drop to 14/20 for the 2008 model year. The industry's top gas-guzzler, the exotic Lamborghini Murcielago LP640 sports car will see a drop from 9/14 to an even-more-pitiful 8/13 mpg.

Hybrid gas/electric-powered models are expected to see more-profound reductions in their fuel economy ratings. As it stands today, the EPA's ratings for hybrid vehicles tend to be over-stated by a factor of at least 20 percent. This discrepancy can be wider yet if a motorist drives primarily on the highway, where hybrids tend to be less efficient than in stop-and-go city driving conditions (during which the electric motor shoulders more of the effort).

For example, the Toyota Prius, which is estimated for 2007 at an industry leading 51-city/60-highway mpg is seeing those figures fall to 45/48, while its closest competitor, the Honda Civic Hybrid, will have its mileage estimates revised from its 2007 rating of 49/51 to 40/45 for 2008.

However, while the new system should afford a more-accurate prediction of a vehicle's fuel consumption--which is of obvious benefit to new-vehicle shoppers-the revisions will have no bearing on how new models are evaluated to meet federally mandated Corporate Average Fuel Economy requirements, which stand at an average of 27.5 mpg for cars and 21.6 mpg for trucks in each automakers' fleet.

Thus, while new-vehicle shoppers will be provided with more-realistic ratings for 2008 models and beyond, the government will continue to evaluate cars and trucks for CAFE purposes under a system that produces unnaturally inflated fuel economy figures (higher, in fact, than those under the prior reporting system for consumers). Environmentalists understandably feel that the fix is in for the auto industry.

"It's an absurd situation," says Therese Langer, transportation program director for the American Council for an Energy-Efficient Economy. "The numbers generated to demonstrate manufacturers' CAFE compliance have little basis in reality."

 
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